1. Field of the Invention
The present invention relates to a semiconductor device and a radiation image pickup system having the semiconductor device, and particularly relates to a semiconductor device in which a separation preventing layer for preventing a protective layer and a scintillator from being separated from each other is formed between the protective layer and the scintillator, and a radiation image pickup system having the semiconductor device.
2. Related Background Art
In recent years, X-ray area sensors have been published by various companies in the development of filmless roentgenography. The systems of the X-ray area sensors are typically divided into a direct system and an indirect system. The direct system is of a type in which an X-ray is directly converted into an electric signal to be read. The indirect system is of a type in which an X-ray is once converted by a wavelength converting member into a radiation having a different wavelength such as visible light, etc., and the radiation with the converted wavelength (e.g., visible light) is then converted into an electric signal by a photoelectric conversion element sensitive to the converted wavelength to be read.
FIG. 1 is a schematic sectional view for explaining an example of an X-ray area sensor of the indirect system. In FIG. 1, reference numeral 401 denotes a substrate such as of glass; 402 a photoelectric converting portion such as an MIS type photosensor using amorphous silicon; and 403 a TFT switch portion. Reference numeral 411 denotes a protective layer of a nitride, etc.; 421 a scintillator of cesium iodide (CsI), etc. as a wavelength converting member; and 422 a reflective film of aluminum, etc.
With the X-ray area sensor shown in FIG. 1, the photosensor portion (photoelectric converting portion) 402, the TFT switch portion 403 and the protective layer 411 are normally formed on the glass substrate 401; the scintillator 421 comprised of cesium iodide, etc. is directly evaporated on the protective layer 411: and the reflective film 422 is directly evaporated or adhered (no adhesive layer is illustrated) onto the scintillator 421, thus completing the X-ray area sensor.
When an X-ray is made incident on the thus completed X-ray area sensor from the upper side in FIG. 1, the X-ray passes through the reflective film 422 and is absorbed by the scintillator 421. The scintillator 421 absorbing the X-ray emits visible light within a bulk in all directions. At this time, since in the scintillator 421 comprised of cesium iodide, crystals are grown in columnar shapes as shown in FIG. 1, the light emitted within the bulk is finally advanced in the columnar direction as in the principle of an optical fiber while being reflected at grain boundaries, and almost all of the light is converged to the photosensor portion 402 and the TFT switch portion 403 located on the lower side in FIG. 1. Therefore, the photosensitivity and resolution can be improved.
As described above, with the X-ray area sensor, the scintillator may be directly evaporated on the protective layer, and in particular, cesium iodide as a material of the scintillator is formed by evaporation so as to obtain the characteristics of the columnar crystals. However, because the bonding force of cesium iodide to a substance of a low thermal conductivity is small, the bonding of cesium iodide to such a substance is subject to peeling off, thus resulting in separation. The protective layer is generally made of a substance of a low thermal conductivity. Accordingly, with the configuration shown in FIG. 1, since the bonding force of the scintillator and the protective layer is small, the scintillator and the protective layer may be separated from each other due to peeling off. Therefore, there has been a room for improvement in impact resistance and reliability in a semiconductor device having an X-ray area sensor.
The protective layer also has a function of maintaining the device characteristics, blocking diffusion of an impurity from cesium iodide to the photoelectric converting portion, the switch portion, etc., and preventing penetration of water from the outside. However, if the bonding force of the protective layer and the scintillator is small, the freedom of choice of the material for the protective layer may be reduced, thus placing restrictions on design and manufacture of X-ray area sensors.
An object of the present invention is to provide a semiconductor device having a structure in which a wavelength converting member is difficult to be separated from the main body of the semiconductor device.
Further, another object of the present invention is to provide a semiconductor device with excellent impact resistance and reliability.
According to the present invention, there is provided a semiconductor device comprising a photoelectric converting portion, a protective layer provided on the photoelectric converting portion, a wavelength converting member provided on the protective layer, and a separation preventing layer provided between the protective layer and the wavelength converting member.
According to the present invention, there is also provided a radiation image pickup system comprising the above mentioned semiconductor device, a signal processing means for processing a signal from the semiconductor device, a recording means for recording a signal from the signal processing means, a display means for displaying a signal from the signal processing means, a transfer means for transferring a signal from the signal processing means, and a radiation source for irradiating the semiconductor device with a radiation.